Why are There Different Blood Types?

Written By Devika Chauhan

If you’ve ever donated blood or have gone for a blood test, you would know that each person belongs to various blood groups. The crimson red fluid that runs through our network of veins and arteries, is categorized as 8 different blood types. These include; A positive (A+), A negative (A-), B positive (B+), B negative (B-), AB positive (AB+), AB negative (AB-), O positive (O+), and O negative (O-). 

Red blood cells (RBCs) contain hemoglobin, which binds to oxygen in order to transport it through the circulatory system. On the outside of the cell membrane, another protein called antigens, can be found. Antigens communicate with white blood cells (WBCs) and hence are used as identification signalers for the WBCS. This allows the WBCS to recognize the RBCs as the body’s cells rather than mistaking them for a foreign, and potentially harmful substance. 

Blood types are determined by which antigen (either A or B) is possessed by the RBCs in one’s blood. This is known as the ABO system. 

Type A Blood = RBCs have an antigen

Type B Blood = RBCs have B Antigen

Type AB Blood = RBCs have both A and B Antigens

Type O Blood = RBCs have neither A nor B Antigens

Now, what’s important to understand is how a blood type is classified as “positive” or “negative.” This is determined by the Rhesus or Rh factor in the D antigen. Rh+ or Rh - refers to the presence or absence of the D antigen respectively, in the Rh blood group system. Outside of the ABO system, there exist over 30 unique and rare blood groups. A blood type is considered as rare when it exists at a rate of 1 per 1,000 people or fewer. The rarest blood type is Rh-null with fewer than 50 people in the world having this type of blood, hence giving it the name, “golden blood.”

Knowing one’s blood type is extremely important as it can be a matter of life or death. If one person donates blood to another person with a different blood type, the WBCs in the recipient's body will attack the donated blood, as it perceives it as a foreign material. This will then cause blood clots, restricting the flow of blood, and possibly putting the recipient's life at stake. Therefore, only those with the same blood type can donate and receive blood from each other, when needed for blood transfusions or organ transplants. However, people with the blood type of O negative are able to safely donate their blood to any blood group, thus known as the universal donor. Those with a blood type of AB positive can safely receive blood from any blood group, hence they are known as the universal recipients. 

References

Cleveland Clinic. (2023, March 14). Blood Types: Differences, Rarity and Compatibility. Cleveland Clinic. https://my.clevelandclinic.org/health/treatments/21213-blood-types

TED-Ed. (2015). Why do blood types matter? - Natalie S. Hodge [YouTube Video]. In YouTube.

Written By Devika Chauhan from MEDILOQUY